gSPBranchLessZ [Macro]

Function

gSPBranchLessZ

Conditionally branches the display list

Syntax

#include <ultra64.h>        /* gbi.h */
gSPBranchLessZ(
        Gfx *gdl,
        Gfx *branchdl,
        u32 vtx,
        f32 zval,
        f32 near,
        f32 far,
        s32 flag)
gsSPBranchLessZ(
        Gfx *branchdl,
        u32 vtx,
        f32 zval,
        f32 near,
        f32 far,
        s32 flag)

Arguments

gdl

the display list pointer.

branchdl

the pointer to the display list branch.

vtx

the vertex (index in the vertex buffer).

zval

the Z value which becomes the branch condition.

near

the location of the near plane (a value specified by either guPerspective or guOrtho).

far

the location of the far plane (a value specified by either guPerspective or guOrtho).

flag

the projection method:

G_BZ_PERSP (Perspective projection)

G_BZ_ORTHO (Orthogonal projection)

Description

Conditionally branches the display list. When the depth value of the vertex specified by vtx is less than or equal to zval, the display list is branched to the display list indicated by branchdl. When it is more than zval, nothing is done. This provides an easy way to perform LOD processing on a model.

Note

This macro assumes that the values of the two viewport Z-direction arguments vp.vscale[2] and vp.vtrans[2] (see g*SPViewport) are both G_MAXZ/2. When this is the case, the depth value is greater than 0 and less than G_MAXZ. Normally the depth value does not need to be changed in an application. However, if you are going to change this value, please use the g*SPBranchLessZrg macro.

Example

The following is an example of a model with 3-level LOD: 
Gfx model_near[ ] = {		// Model's distance less than or equal to 200.
	..........
	gsSPEndDisplayList( ),
};
Gfx model_mid[ ] = {		// Model's distance between 201 and 800.
	..........
	gsSPEndDisplayList( ),
};
Gfx model_far[ ] = {		// Model's distance between 801 and 1600.
	..........
	gsSPEndDisplayList( ),
};
Gfx model[ ] = {
	gsSPVertex(testvtx, 1, 0),
	gsSPBranchLessZ(model_near, 0,  200, 32, 2000, G_BZ_PERSP),  // Model's distance less than or equal to 200.
	gsSPBranchLessZ(model_mid,  0,  800, 32, 2000, G_BZ_PERSP),  // Model's distance between 201 and 800.
	gsSPBranchLessZ(model_far,  0, 1600, 32, 2000, G_BZ_PERSP),  // Model's distance between 801 and 1600.
	gsSPEndDisplayList( ),                                         // Model's distance greater than 1600.
};

See Also

gSPBranchLessZrg

Revision History

02/01/99 Entirely revised.